1. Field of the Invention
This invention relates generally to apparatus and methods used for seismic surveying, and more particularly to a cable connector and method for assembling a seismic survey system.
2. Description of the Related Art
Seismic surveys are conducted by deploying a large array of seismic sensors over a surface portion of the earth. Typically, these arrays cover 50 square miles and may include 2000 to 5000 seismic sensors. An energy source (buried dynamite for example) is discharged within the array and the resulting shock wave is an acoustic wave that propagates through the subsurface structures of the earth. A portion of the wave is reflected at underground discontinuities, such as oil and gas reservoirs. These reflections are then sensed at the surface by the sensor array and recorded. Such sensing and recording are referred to herein as seismic data acquisition, which might also be performed in a passive mode without an active seismic energy source.
A three dimensional map, or seismic image, of the subsurface structures is generated by moving the energy source to different locations while collecting data within the array. This map is then used to make decisions about drilling locations, reservoir size and pay zone depth.
The typical seismic surveying system includes a large number of sensors cabled together in an array and to a field box. Any number of these sensor arrays and boxes are then coupled together depending on the size of the survey area to form a spread. And the field boxes and sensor arrays are then coupled to a central controller/recorder.
The traditional sensor has long been a geophone velocity measuring sensor. Today, accelerometers are becoming more widely utilized, and multi-axis, or multi-component, accelerometers are emerging. Multi-component (three axis) sensing has shown to give superior images of the subsurface as compared to single component sensing. Multi-component sensing, however, has not been economically viable in the past due to the added cost of the recording system and implementation problems with multi-component analog sensors. With the advent of the multi-component digital sensor, such as the Vectorseis® sensor module available from Input/Output, Inc., Stafford, Tex., a multi-component digital sensor is now practical. Multi-component recording, however, requires higher sensor density than single component recording to realize the full advantage seismic imaging with multi-component recording.
The most popular architecture of current seismic data acquisition systems is a point-to-point cable connection of all of the sensors. Output signals from the sensors are usually digitized and relayed down the cable lines to a high-speed backbone field processing device or field box. The high-speed backbone is typically connected in a point-to-point relay fashion with other field boxes and then to a central recording system where all of the data are recorded onto magnetic tape.
Seismic data may be recorded at the field boxes for later retrieval, and in some cases a leading field box will communicate command and control information with the central recorder over a radio link. Still, there exists miles of cabling between the individual field boxes, between the field boxes and sensor lines, and between the sensors.
The typical cable system architecture results in more than 100 miles of cable deployed over the survey area. The deployment of miles of cable over varying terrain requires significant equipment and labor, often in harsh environments.
FIG. 1 depicts a typical seismic data acquisition system 100. The typical system 100 includes an array (“string”) of spaced-apart seismic sensor units 102. Each string of sensors is typically coupled via cabling to a data acquisition device (“field box”) 103, and several data acquisition devices and associated string of sensors are coupled via cabling 110 to form a line 108, which is then coupled via cabling 110 to a line tap or (“crossline unit”) 104. Several crossline units and associated lines are usually coupled together and then to a central controller 106 housing a main recorder (not shown). The typical sensor unit 102 in use today is a velocity geophone used to measure acoustic wave velocity traveling in the earth. Recently, and as noted above, acceleration sensors (accelerometers) are finding more widespread acceptance for measuring acceleration associated with the acoustic wave. Each sensor unit might comprise a single sensor element or more than one sensor element for multi-component seismic sensor units.
The sensors 102 are usually spaced at least on the order of tens of meters, e.g., 13.8–220.0 feet. Each of the crossline units 104 typically performs some signal processing and then stores the processed signals as seismic information for later retrieval as explained above. The crossline units 104 are each coupled, either in parallel or in series with one of the units 104a serving as an interface with between the central controller 106 and all crossline units 104.
Cables 110 must be connected to each other, to field boxes 103, to crossline units 104 and to the controller/recorder 106 to make up the system 100. Consequently, the cables and boxes must utilize connectors 112 that enable assembling the system 100 and that enable disassembling for moving the system 100 to a new survey location and after a survey is complete.
Connectors in the typical seismic system have long been a source of frustration in the field. Harsh environmental conditions, debris and complexity all contribute to difficulty in making up the system and in disassembling the system. Temperatures may be on the order of 40° below zero Fahrenheit or lower and upwards of 110° or more. Furthermore, seismic cables are often connected and disconnected during times of freezing rain and/or snow.
The typical connector often seizes under harsh conditions making connections and disconnections difficult if not impossible. The typical connector also usually has different connector types for corresponding connector halves and seismic crews must have both types of connector halves at the ready for field repair.
Some connectors today use threaded connector locking rings with a male side threaded into a threaded female receptacle. These connectors require the operator to press the electrical pins and sockets together and then the locking ring is rotated multiple rotations to complete the connections.
Disconnecting the connector is accomplished by unscrewing the locking ring and then the operator can pull the electrical connections apart. When the connector is difficult to disconnect due to debris, freezing or misalignment, the operator is often tempted to pull on the cables. Pulling cables rather than connector housings leads to damage to the electrical components.
These threaded connectors also suffer from the fact that different structural parts are used for each half of the coupling. That is, a male half and a female half. Repairs require both components be available, which sometimes leads to waste where one half is not needed for a repair. These non-hermaphrodite connectors also require different machining in manufacturing making manufacturing more expensive.
Attempts have been made to address the problems associated with the non-hermaphrodite connector. Connectors have been proposed that provide hermaphrodite electrical and mechanical components, and proposed connectors attempt to address the issues associated with longitudinal force application.
One example of a hermaphrodite connector assembly is U.S. Pat. No. 6,447,319 to Jaques Bodin. The connector described in the '319 patent is used in making up geophysical data acquisition and processing systems. The connector coupling consists of two identical electrically and mechanically fitting male/female connectors, each connector comprising a body bearing a set of connection pins and a ring enclosing the connector body base and capable of being moved in rotation relatively to the body, the connector ring comprising a raised motif for plugging in the associated connector. Each connector comprises two stages of raised motif of which one front raised stage substantially matching the ring motif to co-operate with the associated connector ring motif in a locked position of the device and a rear stage to co-operate with the ring motif of the same connector in a retracted position of the ring.
One problem with a connector according to the '319 patent is that initial longitudinal coupling force must be applied by a person mating the connectors. Another problem is that a corresponding decoupling force must be applied after the connectors are unlocked. Starting from a situation in which two aligned connectors according to the '319 patent have their ring in the retracted position, the front faces of the two connectors are moved towards each other in translation. The projecting members of one of the two connectors (the members 140 and 150 in FIG. 1 of the '319 reference) are engaged in the spaces between the like members of the other connector. The members therefore interpenetrate in a complementary manner.
The '319 reference teaches that during interengagement of the projecting members, the chimneys of each connector enter the cavities of the other connector and the male and female contacts of the two connectors connect the four wires of the cable of each connector in pairs.
Once this translatory interengagement has been completed, the device is locked by turning at least one of the rings approximately 90° to engage the projecting part of the ring in the grooves on the body of the other connector.
Co-operation of the helicoidal ramps on the projecting parts of the ring with those in the grooves of the body of the other connector converts this 90° rotation into helicoidal movement of the ring of one connector relative to the body of the other connector this tightens the mechanical connection, which is then “screwed tight”.
U.S. Pat. No. 4,037,902 describes a hermaphrodite cable connector assembly that may be used in seismic survey systems. The '902 reference teaches a multiple connector plug having a front or mating end, and a back or cable end, comprising a cylindrical body having a contact assembly, including means to support a plurality of electrical contacts. The contact assembly surrounds and is sealed to the body, and has projections adapted to mesh with the corresponding projections on the contact assembly of a mating plug, so as to relatively index the two plugs and their contacts. The plug has a cylindrical tubular locking ring with diametrically disposed extensions which mesh with the extensions of the locking ring on a mating plug. There are sloping grooves and ridges on the projections so that as the locking ring is rotated clockwise with respect to a locking ring on a mating plug, the two plugs will be pulled and locked together. When the locking rings are turned counterclockwise with respect to each other, cam surfaces on the ends of the projections act to unlock and separate the two plugs.
FIG. 8 in the '902 reference, illustrates the meshing of the interior ridge 88A into the exterior slot 86, and the exterior ridge 88 into the interior slot 86A.
At the start, these meshing ridges and slots (or cams 86, 86A) mesh at the starting edges 87, 87A, then as the locking rings are rotated clockwise with respect to each other, according to the arrows 98, 98A, they begin to pull the locking rings together, and with them, the plugs.
The outer edges 89 of the projections are formed with cam slopes 90. By counterclockwise rotation of the locking rings, the cam surfaces come into play and separate the plugs.
FIG. 8 of the '902 reference shows that the plugs are locked by sliding the extensions 84 in the direction of the arrows 98, 98A. This corresponds to clockwise rotation of the locking rings with respect to each other. A turn of about 90° is required to close and lock the plugs.
The '902 reference illustrates the action of unlocking in FIG. 6, which shows the locking rings unmeshed, but the plug contacts still meshed. Another 30° of counterclockwise rotation in the direction of arrows 99, 99A will cause the two pairs of cam surfaces 90, 90A to press the two plugs apart, until the contacts are separated.
It is important to note the interaction of cam surfaces 90 and 90A for providing longitudinal forces. Such large surface area interaction will provide a corresponding frictional force that opposes the rotation of the locking rings.
The typical hermaphrodite connector that reduces the need for multiple connector type still suffers from seizing. The proposed connectors attempting to reduce longitudinal force requirements still suffer seizing due to high interface friction and large surface area contact.
Debris such as mud and ice can also make mating the typical hermaphrodite connector difficult. Debris in the grooves can block interfacing ridges and the field crew must waste time to clean the connector in order to successfully mate the connector.
In view of the problems associated with the typical connectors described above, there is a need for a seismic cable connector that is hermaphrodite, does not require longitudinal input force from a technician for connecting and disconnecting, and is less susceptible to debris-related failures in the mating structure.